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The ACI 209 creep model is used to account for creep for all design codes, including AS3600. ACI 209 assumes that the initial loading is applied at 7 days. AS 3600 assumes a different time for initial load application, so the creep factor must be adjusted for an initial loading time of 7 days when that design code is selected.
You are correct that using the AS3600 adjusted creep factors may be significantly different than the suggested creep factors in ACI 209. Also, RAM Concept may be using slightly different values at times other than the ultimate creep due to using a curve from a different creep model. However, RAM Concept is ultimately using input values that are required by AS3600 and those values should be input into the program.